1. Field of the Invention
The present invention relates to a screw-nut feed mechanism, and more particularly to a screw-nut feed mechanism suitable for use in a telescopically adjustable steering column mechanism for motor vehicles.
2. Description of the Prior Art
In Japanese Utility Model Early Publication 60-182278, there has been proposed a telescopically adjustable steering column mechanism of the motor drive type which includes an outer hollow steering shaft rotatably carried on a stationary structure, an inner tubular steering shaft axially slidably disposed in the outer steering shaft for rotation therewith, a telescopic shaft rotatably disposed in the inner steering shaft for axial movement therewith, and a feed screw shaft having one end connected to the outer steering shaft and an externally threaded portion in engagement with an internally threaded portion of the telescopic shaft. In the steering column mechanism, a conical member is axially slidably coupled with the feed screw shaft and threaded into the inner end of the inner steering shaft. The conical member acts to eliminate an annular space between the outer and inner steering shafts during rotation of the telescopic shaft but does not effect to minimize or eliminate clearance spaces between the mating threads. To minimize or eliminate all of the clearance spaces between the mating threads, the respective threaded portions of the shafts must be formed with a very high degree of accuracy. This results in an increase of the production cost of the steering mechanism.